Double‐layer capacitance measurements of self‐assembled layers on gold electrodes

Abstract The double‐layer capacitance of self‐assembled unsubstituted and ω‐substituted n‐alkanethiol layers on gold electrodes was studied using a potential step technique. A four‐element equivalent circuit model was used for the evaluation of the current response. The double‐layer capacitance and the conductivity were both found to decrease with increasing chain length for alkanethiol homologues. Substitution with COOH, OH, and NH2 in the ω‐position caused the double‐layer capacitance to rise dramatically, whereas the general pattern of decreasing capacitance with increasing chain length was confirmed for a series of homologue ω‐mercaptoalcohols. The effect of polar substituents is explained by the introduction of permanent dipoles into the self‐assembled layers. The capacitance was independent of the applied potential for dodecanethiol but increased with voltage for butanethiol when tested in the range of −200 to 500 mV versus Ag/AgCl. Buffer strength had little influence on the double‐layer capacitance above 5 mM (phosphate buffer, pH 7.0). The self‐assembly of mercaptoethanol was completed within 3 minutes from an aqueous solution and that of alkanethiols within 10 minutes using acetone solutions. The electrodes were stable for at least several hours.